1. Field of the Invention
The present invention relates to a golf ball. More particularly, the present invention relates to an improvement in the sectional shape of a dimple.
2. Description of the Related Art
A golf ball has a large number of dimples on a surface thereof. The role of the dimples resides in one aspect that such dimples disturb an air stream around the golf ball during the flight ball to accelerate the transition of a turbulent flow at a boundary layer, thereby causing a turbulent flow separation (which will be hereinafter referred to as a “dimple effect”). The acceleration of the transition of the turbulent flow causes a separating point of air from the golf ball to be shifted backward so that a drag coefficient (Cd) is reduced, resulting in an increase in the flight distance of the golf ball. In addition, the acceleration of the transition of the turbulent flow increases a differential between upper and lower separating points of the golf ball which is caused by a back spin. Consequently, a lift acting on the golf ball is increased. An improvement in the sectional shape of the dimple intended for an enhancement in a flight performance has variously been proposed.
Japanese Laid-Open Patent Publication No. Hei 5-237202 (1993/237202) has disclosed a golf ball in which the edge angles of dimples having different sectional shapes from each other are equal. Japanese Laid-Open Patent Publication No. Hei 9-285566 (1997/285566) has disclosed a golf ball in which the inclination angle of a tangential line with respect to a surface in the edge of a dimple is set within a predetermined range. Japanese Laid-Open Patent Publication No. Hei 11-89967 (1999/89967) has disclosed a golf ball comprising a dimple having an edge angle of 30 degrees or less. Japanese Laid-Open Patent Publication No. 2000-279553 has disclosed a golf ball comprising a dimple having a special sectional shape. These techniques relate to the shape of a portion provided on the inside of an edge.
A golf player is most concerned about the flight distance of a golf ball. In respect of an enhancement in the flight distance, the sectional shape of a dimple has room for an improvement. It is an object of the present invention to improve the flight performance of a golf ball.